Conventionally, as a device that displays an image, a liquid crystal display device that utilizes the properties of liquid crystal is wildly used. As an example of a backlight unit used in the liquid crystal display device or the like, a backlight unit that utilizes light-emitting diodes (LEDs) as a light source is disclosed in, for example, patent document 1.
In general, in the backlight unit using LEDs as a light source, a plurality of LEDs are connected to one or a plurality of LED drivers (driver devices). The LED driver receives lighting control information (for example, information indicating a duty ratio used when the turning on and off is controlled by PWM) from an additionally provided control device, and turns on the LED connected thereto according to the lighting control information. As the LED driver, there is also an LED driver that includes a plurality of control channels to which one or a plurality of LEDs are connected.
In the image display device including the backlight unit described above, it is likely that, for each of one or a plurality of LEDs, it is desirable to independently control the state of lighting. In one example, it is likely that, in order to enhance performance in displaying a moving image in the image display device, it is desirable to control the state of the lighting of each LED group consisting of LEDs corresponding to one section (one row or a plurality of continuous rows) in a display region.
Hence, there is an image display device which includes a plurality of LED drivers and in which each of the LED drivers receives a different piece of lighting control information. However, when the control device feeds the lighting control information, if signals carrying such information are fed in parallel to the individual LED drivers, the number of transmission lines necessary to feed the signals is increased.
Furthermore, when the total number of LED drives provided is not fixed (for example, when the number of LED drivers is likely to be increased or decreased afterward), it is difficult to provide, in the control device, an exact number of terminals for forming the transmission lines. If an excessive number of terminals are provided, part of the terminals are wasted whereas, if the number of terminals provided is low, it may be impossible to additionally increase the number of LED drivers or the like.
With respect to this problem, when the individual LED drivers are previously connected in cascade and the signals carrying the lighting control information are fed over the transmission line (cascade line) of this cascade connection, it is possible to prevent the increase in the necessary number of transmission lines. Furthermore, since, even if the total number of LED drivers provided is not fixed, the number of transmission lines is not changed, it is easy to provide an exact number of terminals for forming the transmission lines. Hence, the method of transmitting the lighting control information over the cascade line as described above may be employed.